Some web pages are (correctly) linked into multiple indexes, but can only have one prefix.

An app that only runs on a K4 or K5 would go into its "type of app" index, and into the K4 and K5 indexes.

Kindle models K20 and K33 do not exist outside of this post, just example numbers.

Adding a serial port to a K20 might be in both Hardware and in K20 but the post can only have one prefix tag and could only go a single place.

So there would still have to be a "Master Index" of some sort, be it the leading post of this thread or a Wiki page.

Maybe then all of the prefixes should click-through to the "Master Index" - however the "Master Index" was implemented.

Consider the situation right now (as first time visitor to site) - - -

Person pulls up a thread prefixed Hardware and reads that it is about the serial port on the K20.
Thinks: "I want one of those for my K33".

Now what does this person do?

If observant the visitor might have noticed the titles of the stickies when they first landed on this site (yeah, right!);
Might even have remembered there was one titled something about a master prefix index. (yeah, maybe!)

Having surmounted those mental challenges, which of the master index lines does this person pick?
Hardware (which was the tag), K20 (which was in the subject), K33 (which is the only thing this visitor is interested in)?

Dealing now with the "instant gratification generation" they will pick: K33
But the K33 didn't exist when the O.P. put up their post - no link.
Pick: Hardware?
Hmm... There is a Wiki:Hardware:Serial Port (about 6 hours old now).
No K33 mentioned, the K33 didn't exist when the O.P. listed it under Wiki:Hardware:Serial Port:K20

Well, even though a single destination for a single prefix would have landed this visitor at Wiki:Hardware it wouldn't have given the "instant answer" but at least all of the above mental handsprings could have been avoided.

And if the O.P. had not indexed their post at all?

There are 156,000 members here - think they can all "get it right"?

At least landing the new visitor on the "most significant of many" by a click-able prefix would not have made the situation any worse.
The new visitor would still have to use the Wiki navigation bar to go searching for K33 or K20 or ...

Translation:
Technically you are correct, one prefix to many destinations can't be programmed;

In practice, one prefix to "most significant" Wiki page + the page top navigation aid would be better (in my opinion) than what we have now.

But those are just our opinions, still to be heard from is the other 156,000-2 members.